A heat developable light sensitive material comprising a silver halide as the light-sensitive component is known in the art. Examples of such heat developable light-sensitive materials are described in Shaskin Kogaku no Kiso (Elementary Photographic Engineering), (Non-silver photography), Corona, 1982, pp. 242-255, Eizo Joho, April 1978, page 40, Neblets, Handbook of Photography and Reprography, 7th ed., Van Nostrand Reinhold Company, pp. 32-33, U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020, and 3,457,075, British Patents 1,131,108 and 1,167,777, and Research Disclosure, June 1978, pp. 9-15.
Many approaches have been suggested to obtain color images in a heat development process.
For example, a process which comprises the coupling of a coupler and an oxidation product of a developing agent produced by reduction of silver halides to form color images is described in U.S. Pat. Nos. 3,531,286, 3,761,270, and 4,021,240, Belgian Patent 802,510, and Research Disclosure, No. 13742.
A process which comprises a silver dye bleach process using silver halides to form positive color images in a heat development process is described in U.S. Pat. No. 4,235,957 and Research Disclosure, Nos. 14433 and 15227.
A further process has been suggested which comprises allowing a diffusible dye to form or be released imagewise from a dye-providing compound upon heat development of silver halides and the transferring the diffusible dye to a dye fixing element containing a mordant with a solvent such as water, a high boiling organic solvent, or a hydrophilic thermal solvent incorporated in the dye fixing element. In another embodiment of this process, the mobile dye is heat-diffusible or sublimable. Such a heat-diffusible or sublimable dye is transferred to a dye receiving element on the support. In this process, both negative and positive dye images can be obtained with respect to the same original by altering the kind of dye providing compound or silver halide emulsion used as described in U.S. Pat. Nos. 4,463,079, 4,474,867, 4,478,927, 4,507,380, 4,500,626, and 4,483,914, JP-A-58-149046 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-58-149047, JP-A-59-152440, JP-A-59-154445, JP-A-59-165054, JP-A-59-180548, JP-A-59-168439, JP-A-59-174832, JP-A-59-174833, JP-A-59-174834, JP-A-59-174835, JP-A-62-65038, JP-A-61-23245, and European Patents 210,660A2 and 220,746A2.
The use of paper as a support in such a heat developable light-sensitive material is somewhat advantageous. For example, a paper support is cheaper than a polymer film support such as polyethylene terephthalate film. Furthermore, a light-sensitive material comprising such a paper support can be easily discarded after use. However, such a light-sensitive material comprising a paper support is disadvantageous in that it is highly subject to fog during processing or it is highly subject to fog during storage. Many factors are believed to cause fog in silver halide. For example, it is believed that sodium sulfide, sulfites, or bleaching agents incorporated in pulp, or sizing agents, paper strength improvers, softeners or dimensional stabilizers incorporated during paper making contain a substance which causes fog in silver halide.
Particularly, heat developable light-sensitive materials are more subject to fog and the effects caused by the presence of a slight amount of the above components contained in a paper support, as compared to ordinary photographic light-sensitive materials because they are developed at elevated temperatures.
In general, a paper support for use in a photographic light-sensitive material is often laminated with polyethylene or the like to prevent water from penetrating into the support during processing so that the light-sensitive material can be rapidly dried after processing. However, this approach is disadvantageous in that the above described fogging substances diffuse into the emulsion layer through minute defects (holes) in the polyethylene film and cause fogging in the light-sensitive material during prolonged storage.